Document use of CC and CFLAGS in more detail (bug 20980, bug 21234)

[Joseph Myers]

On Tue, 6 Feb 2018, DJ Delorie wrote:

> 
> Joseph Myers <joseph@codesourcery.com> writes:
> > +   It may also be useful to pass 'CC=COMPILER' and 'CFLAGS=FLAGS'
> > +arguments to 'configure'.  'CC' selects the C compiler that will be
> 
> The first example of how to do this is 270 lines later...
> 
> I suspect people familiar with GNU configure might assume you meant
> 
> $ CC=... configure

The recommended approach has been "configure CC=..." not "CC=... 
configure" ever since autoconf 2.50 (released 2001).

Passing in the environment does tend to work (modulo possible errors if 
the value is different when config.status gets run) and I don't think it's 
necessary for the glibc-specific instructions to emphasise the existence 
of this deprecation, but I don't think the instructions should use the 
deprecated form either - they should use the preferred modern form.

-- 
Joseph S. Myers
joseph@codesourcery.com